[-nocturne=-]

Just figured I'd say that as far as I know, TMU keys do not work yet for TMN validation (keep an eye on the official TM forum though).

Basically, you can customize your car, horn, and avatar in TMN, but unless you buy a retail copy of one of their previous games (TM:Original or TM:Sunrise) and register that game's cd key for TMN by logging into the TMN website with the same profile you use online, nobody else but you will see your customizations.